"Twelve years a slave" was originally published in 1853 - this later printing, in 1859, was digitized from the Library of Congress general collections. (An earlier edition is in the custody of the Rare Book & Special Collections Division of the Library.) This 1859 printing has the same illustrations and is in most respects the same as the 1853 edition. The main difference appears to be the title page since publisher information is presented differently.
http://lccn.loc.gov/13004011 is the record in the Library of Congress online catalog for this digitized book.